Rapid assembly, concentric mating stent, tissue heart valve with enhanced clamping and tissue alignment

ABSTRACT

A concentric mating stent tissue heart valve which is capable of being assembled with a variety of tissue sources is provided. A plurality of prefabricated kits are also provided which enable the valve to be assembled with autogenous tissue in the limited time, i.e., 10 minutes or less, available in the operating room. The inner stent can be configured with a plurality of tissue alignment members extending outward from the inner stent to corresponding holes cut in the tissue. The outer stent can be configured with posts adapted for nesting with corresponding inner stent posts, and integrated with self-adjusting tensioning means, to exert a substantially uniform clamping force on the tissue sufficient to secure the tissue between the stents.

This is a divisional of copending application Ser. No. 07/646,001, filedon Jan. 24, 1991, now U.S. Pat No. 5,163,955.

BACKGROUND OF THE INVENTION

I. Field of the Invention

This invention relates generally to a rapid assembly, concentric andflexible mating stent, tissue heart valve which substantiallysubstitutes clamping of the tissue for sewing, and more specifically, tosuch a valve which can be assembled from prefabricated kits by anon-surgeon in the limited time available in an operating room, which isconfigured to substantially uniformly clamp the tissue between thestents and securely hold the tissue in place after valve assembly, whichis also configured with tissue alignment members to provide enhancedalignment of the tissue between the stents during valve assembly. Aftervalve assembly, the tissue is held in place by the clamping force of thestents.

II. Background of the Invention

Several types of heart valves are presently available for use inreplacing diseased or malfunctioning heart valves in humans.

One such valve is an animal tissue valve, constructed utilizing bovinetissue or porcine aortic valve tissue or the like. These valvestypically must be constructed by a trained specialist in a laboratorysetting well in advance of when they will be needed to replace adiseased or malfunctioning human heart valve, and then stored in analdehyde solution until they are needed.

Although these valves have proven to have acceptable hemodynamics, theytypically suffer from a durability problem, which requires that thesevalves be replaced after about five to ten years of use. This is asignificant problem because, after a first implant of a heart valve,subsequent implants in the same area of the heart are more difficult andrisky to the patient.

The durability problem in animal tissue valves arises from two sources.First, the tissue is typically treated with glutaraldehyde or the liketo attenuate the antigenicity of the tissue, and this will tan thetissue to a leather-like consistency. As a result, the tissue willbecome more inflexible, and over time, the valve may wear out from thestress exerted on the valve by the repeated opening and closing of thevalve. Second, the antigenicity of the tissue may generate animmunological response which causes the valve to calcify, rendering itinflexible and susceptible to stress. A treatment with glutaraldehydesignificantly reduces, but does not completely eliminate, the hostbody's immunological response to the foreign tissue. Animal tissuevalves are typically not recommended for children and young adultsprecisely because they are not durable enough for them. One theory isthat the more active immunological response in children leads to morerapid calcification of these valves, which in turn, causes their reduceddurability in children.

Another problem with animal tissue valves is that they require a trainedspecialist to sew and assemble, and also cannot typically be sewed andassembled in the operating room because of the excessive time required.As a result, they must typically be sewed and assembled in a laboratorysetting well before they are needed to replace a diseased or damagedhuman heart valve. Special facilities are therefore required to processand store the tissue before valve assembly, and to store the assembledvalves until they are needed in the operating room. All these factorsincrease the cost of these valves to the patient.

Another type of valve which is presently available is the mechanicalvalve. This valve is typically constructed from nonbiological materialssuch as hard and durable ceramics, metals, and plastics and the like,and therefore, does not suffer from the durability problem associatedwith animal tissue valves. Because of the nonbiological nature of thesevalves, however, blood clots and the like can easily form on thesevalves, with the attendant risk to the patient that the clot fragmentscould break loose into the arteries, causing an embolism or stroke. Thischaracteristic of mechanical valves is known as thromboembolism. As aresult, a patient into which a mechanical valve has been implanted isrequired to take anticoagulants.

Anticoagulants, however, introduce another set of problems. First, itmay be inconvenient for a patient to take anticoagulants. Second, anyanticoagulant can lead to hemorrhagic complications in some patients,particularly older patients, with the result that mechanical valves maynot be recommended for these patients. Third, some patients may beunreliable about taking their medication, especially in remote areas.

Mechanical valves are also sometimes constructed from expensive materialin short supply such as pyrolytic carbon. This factor also increases thecost of these valves to the patient.

As a result, both animal tissue and mechanical valves have not proven tobe entirely satisfactory, and other valve types have been explored.

Homograft tissue valves have also become available. These valves havenot proven to be entirely satisfactory. Specific limitations of thesevalves include lack of general availability, antigenicity of the tissue,durability being no better than for animal valves, the requirement ofadditional surgical training to implant, the requirement of specialfacilities to harvest and store, the lack of availability in an adequaterange of sizes, and the lack of improved performance over xenografts.Homograft valves, as currently used, also have the potential fortransmitting viral diseases. All these factors result in increased costand risk to the patient.

Autogenous tissue valves, i.e., tissue valves constructed with thepatient's own tissue, have also been explored. Autogenous tissue valves,however, unlike prior art valves, must, as a practical matter, becapable of being assembled during the same surgical procedure in whichthe patient's diseased or damaged valve is replaced. This is becausethese valves cannot practically be assembled in previous surgicalprocedures since they cannot be sized until the annulus of the patient,into which a replacement valve is to be implanted, has been exposed inthe replacement surgical procedure. Although attempts have been made tosize the annulus using X-rays or the like, these methods are onlyapproximate and have not proved reliable.

Assembly during the same surgical procedure, however, requires that theautogenous tissues used in these valves be extracted, and then thevalves themselves be sized and assembled rapidly to avoid anyprolongation of the time that the patient is maintained on acardio-pulmonary bypass. Typically, 10-15 minutes are required to placeanchoring sutures in the valve annulus, and construction of theautogenous tissue valve should be accomplished in that period of time.The autogenous tissue is available for preparation early in the surgicalprocedure for preliminary preparation.

Attempts have been made to construct autogenous tissue valves in thelimited time available while the patient is on the operating table.These attempts, however, were abandoned because of the difficultyencountered in constructing a durable and structurally sound valve inthe limited time available, lack of a standardized repeatable method ofvalve assembly, and poor results with fresh, untreated tissue.

These attempts were abandoned, in part, since the valves wereconstructed and held together typically by the time-consuming anderror-prone method of suturing the tissue to a unitary frame or stent.Not only did this procedure require too much time, i.e., more than 10minutes, to assemble the valve, but it was also found that the risk ofuncertain valve quality, caused by the rushed conditions under which thevalves were assembled, was too high. In fact, poor valve quality causedone early researcher to state: "The construction of the graft in theoperating theatre during surgery, with a limited amount of timeavailable, does not offer the best conditions for the preparation of aperfect valve." See "Replacement of Heart Valves With Frame-MountedTissue Grafts," Ionescu et al., Thorax (1974), Vol. 29, p. 56, at p. 65.This procedure was also expensive and of limited availability, since ittypically could only be performed by skilled surgeons. For all theforegoing reasons, these attempts at constructing autogenous tissuevalves were abandoned.

In U.S. Pat. No. 4,470,157 (the '157 patent), Jack W. Love, one of theinventors herein, pioneered an autogenous valve which utilized matingstents to clamp the tissue between the stents. This patent did notspecifically address the problem of prolapse. This problem occurs whenthe tissue is not uniformly distributed amongst the leaflets of thevalve, the leaflets are not of uniform size, and the co-aptive edges ofthe leaflets do not meet uniformly during valve closure, resulting invalve leakage and undue stress on the leaflets.

Prolapse can be a significant problem, and later attempts to reduce oreliminate prolapse, such as alignment stitches or the like, have notproven successful in completely eliminating prolapse. This is becausethe stitches are difficult to accurately place in an operating roomenvironment where time constraints are important.

Another problem not specifically addressed by the '157 patent was thetendency for the tissue between the stents to slip, due toirregularities in the specific tissue used in the valve interfering withthe clamping force generated by the stents, and due to the lack ofuniformly distributed clamping force both along the annular bases of thestents, and between the stent posts.

U.S. Pat. No. 4,687,483 describes a valve which is assembled byregistering a significant number of pins and studs extending from aninner frame to corresponding holes and slots in an outer frame, securingthe pins with securing washers, and sewing tissue or cloth framecoverings together. Because of the large number of pins and studsinvolved, and the sewing required, this valve is not capable of beingassembled in the limited time available in an operating roomenvironment. Consequently, this valve is not satisfactory for rapidlyassembling an autogenous tissue valve in the operating room.

U.S. Pat. No. 4,192,020 describes a valve which utilizes an adhesivesuch as polyurethane dissolved in tetrahydrofuran to secure fabric towire frames. An adhesive such as this is toxic, and not suitable foraffixing tissue, especially viable human tissue, to a valve.Consequently, this valve is not satisfactory either for use inassembling an autogenous tissue valve.

U.S. Pat. No. 4,501,030 describes a complex valve which utilizes asignificant number of sutures to assemble the valve. Consequently, thisvalve cannot be assembled in the limited time available either.

In sum, for all the foregoing reasons, it is an object of the presentinvention to provide a rapid assembly, flexible and concentric matingstent tissue valve that substantially substitutes clamping for sewing,which is configured to generate a substantially uniform clamping forceon the tissue between the stents in the assembled valve, and which isconfigured to generate a self-adjusting clamping force which adjusts fortissue irregularities. It is a further object to provide a valve whichachieves proper alignment and prevents movement of the tissue duringvalve assembly to prevent prolapse. It is a further object to provide amethod for assembling such a valve which is standardized andreproducible, and which can easily be learned and practiced by anon-surgeon.

Additional objects and advantages will be set forth in the descriptionwhich follows or will be apparent to those or ordinary skill in the artwho practice the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the major components in the valve assembly;

FIGS. 2a-2d illustrate, in detail, the inner stent frame;

FIG. 3 illustrates, in detail, the tissue alignment numbers of the innerstent;

FIGS. 4a-4b illustrate the stent sock;

FIGS. 5a-5d illustrate, in detail, the outer stent frame;

FIGS. 5e-5h illustrate, in detail, the garter spring integrated into theouter stent;

FIG. 6a-6d illustrate the stents when placed in a close mating position;

FIGS. 6e-6g illustrate theoretical ideals for valve dimensions;

FIGS. 7a-7g illustrate the components of the tissue harvesting andannulus sizing kit;

FIGS. 8a-8k illustrate the components of the size-specific stent andvalve assembly kit;

FIG. 8l illustrates the tissue cut into a specific configuration forinsertion into the valve;

FIGS. 9a-9d illustrate the components of outer stent spreading tool; and

FIGS. 10a-10c illustrate embodiments of the valve tester.

SUMMARY OF THE INVENTION

In accordance with the purpose of the invention as broadly describedherein, there is provided a rapid assembly, flexible and concentricmating stent tissue valve that substantially substitutes clamping forsewing, the valve comprising an inner stent, having an annular base witha plurality of posts extending from the base along an axis of the valvein the direction of blood flow, the posts being connected by a scallopededge, and also comprising an outer stent.

The inner stent is configured with a plurality of outward extendingtissue alignment members. During valve assembly, a precisely cut sectionor sections of tissue is prepared with a small number of small,precisely placed holes to be registered with the tissue alignmentmembers. These holes are configured to ensure that the resulting tissueleaflets formed in the assembled valve from the section or sections oftissue will be about the same size and shape. Next, the tissue iswrapped around the inner stent, and the holes in the tissue areregistered with their corresponding tissue alignment members. Thesetissue alignment members will hold the tissue in place during valveassembly, to prevent circumferential, or up or down, movement of thetissue. Valve assembly is then completed by placing an outer stent overthe tissue. The outer stent has integrated within it self-adjustingtensioning means, such as a garter spring or the like, which clamps thestents together while compensating for irregularities in the tissue, andsecures the tissue between the stents.

The outer stent is configured to apply a uniform and self-adjustingclamping force on the tissue. To accomplish this, the outer stent isadvantageously configured to mate closely with the inner stent. It isadvantageously configured, as is the inner stent, with a plurality ofposts extending from an annular base and connected with a scallopededge, which posts are configured for close alignment with correspondinginner stent posts. The posts of the outer stent are advantageouslytapered inward and have windows in the shape of an outline of thecorresponding inner stent posts, which are adapted for alignment withthe outer stent posts. As a result, when the stents are mated, the innerpost stents are biased towards nesting into the outer stent posts. Theresult is a self-adjusting clamping force generated between the posts ofthe stents. Second, the annular base of the outer stent is configuredwith window extensions or the like which split the base of the stent inone or more places. This enables the outer stent to splay open to easilyfit around the inner stent during valve assembly, without damaging thetissue. Moreover, the self-adjusting tensioning means, such as a garterspring or the like, is integrated with the outer stent by fitting itinto a groove extending around the periphery of its annular base. Thisenables the outer stent to apply a self-adjusting clamping force to thetissue between the annular bases of the stents in response to anyirregularities of the tissue at hand. The clamping force generated bythe tapered and windowed stents, and by the self-adjusting tensioningmeans, together is sufficient to secure the tissue between the stentswithout substantial reliance on the tissue alignment members, whoseprimary role substantially ceases after the valve is assembled. Thiscessation of functionality of the alignment members in the assembledvalve is crucial, for it prevents stress from becoming concentrated atthe alignment members, which could lead to the tearing of the tissue,and premature failure of the valve.

A sewing ring is also advantageously integrated into the outer stent toprovide a means for suturing the assembled valve to the annulus of theheart to be fitted with a new valve.

A standardized and reproducible method of assembling the valve in theoperating room is also provided. This is accomplished through the use ofa plurality of pre-fabricated, and possibly disposable kits, whichcontain all the components necessary to harvest the tissue from thepatient, and then assemble the valve. A first sterile, disposable tissueharvesting and annulus sizing kit is provided which contains aroughly-sized tissue template for use in harvesting a section of tissueroughly of the appropriate size. A plurality of obturators of differentsizes is also provided. The technician or surgeon successively plugs theannulus of the heart to be fitted with the obturators until theappropriate size of the annulus is determined.

An optional quick-fix kit is also provided. This kit can be providedseparately, or alternatively, it can be integrated with the first kit.This kit provides a basin and a sterile supply of glutaraldehyde or thelike. This kit provides means for dipping the harvested tissue into theglutaraldehyde solution, thereby quick-fixing it.

A second sterile, disposable size-specific stent and valve assembly kitmatched in size to the specific annulus is then provided containing thesize-specific inner and outer stents, and tools needed to assemble,test, and hold the valve. This kit contains a size specific tissuecutting die to precisely cut the tissue in the flat to an exact patternand size appropriate for the particular annulus to be fitted, and alsoto cut precise holes in the tissue to be registered with the tissuealignment members on the inner stent. This die is configured so that thetissue will not require any additional trimming or processing after itis incorporated into the valve. Additional assembly tools are alsoprovided, consisting of an assembly mandrel and outer stent spreadingtools. To assemble the valve, the inner stent is placed on the mandrel,and the precisely cut tissue is then wrapped around the inner stent suchthat the holes in the tissue are registered with the tissue alignmentmembers. The spreading tools are then used to spread open the outerstent, and place the outer stent over the inner stent without damagingthe tissue.

Next, a valve acceptance tester is provided to test the valve beforeimplanting it. To accomplish this, the valve is placed in the tester,and observed while a known volume of saline or the like is displacedthrough the valve, and then while a known back pressure is applied. Ifthe valve is operating normally, it is then implanted in the human. Toimplant the valve, a valve holder is provided, for use by the surgeonwhen implanting the valve.

These kits pave the way for the assembly of an autogenous valve in thelimited time available. The potential of these valves lies in their lackof antigenicity and potential for viability compared with animal tissuevalves. As a result of their lack of antigenicity, and potential forcontinued viability, these valves also have the potential of being moredurable compared to animal tissue valves.

These valves can be constructed with many sources of tissue, such aspericardial tissue (the tough fibrous tissue surrounding the heart),fascia lata (the tough fibrous casing around the leg muscle), and rectussheath (the tough fibrous casing from the abdominal muscles), andothers. However, pericardial tissue may be the preferred tissue becauseof its proximity to the heart and to the surgical procedure, and becausethe biological form and structure of the human pericardium is similar tothat of the natural valve elements. Another advantage is thatpericardium typically has an identifiable range of thicknesses andstrengths, and, therefore, valves assembled with pericardial tissue arecapable of being assembled with standardized components themselvesconstructed in accordance with uniform specifications.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The components which make up the assembled valve are illustrated inFIG. 1. As illustrated, these components consist of outer stent 1,tissue 2, and inner stent 3.

Turning first to the inner and outer stents, the inner and outer stentspreferably have inner and outer stent frames, respectively, constructedout of a thermoplastic such as DELRIN or the like using injectionmolding techniques to form the entire component using uni-bodyconstruction techniques, instead of using welding or the like to attachany protuberances. Uni-body construction is less risky to the patientthan welding since welded bonds can more easily break, leading to valvecomponents or fragments being injected into the blood stream.

Once constructed, the outer stent frame is integrated with othercomponents such as a sewing ring and a garter spring and both frames arecovered with a fabric such as DACRON or the like, to form the completedinner and outer stents used in valve assembly.

Turning now to FIGS. 2a-2d, additional detail regarding the constructionof the inner stent frame will be described. With reference to FIG. 2a,the inner stent frame is preferably constructed with an annular base 4with a plurality of posts identified with reference numerals 5a, 5b, and5c extending from the annular base along an axis of the valve in thedirection of blood flow through the valve. Preferably, three such postsare provided which are spaced uniformly around the annular base, i.e.,such that the centers of adjacent posts are separated by 120 degrees. Inaddition, the posts are preferably connected by scalloped walls, onesuch wall being identified with reference numeral 5d in the figure. Asillustrated, at least one such post is initially constructed with aplurality of outward facing members 6a, 6b. Preferably, all posts willbe constructed with these members. These members will later be shapedinto tissue alignment members for use in holding the tissue in placewhile the valve is being assembled. Additional detail on one of themembers, i.e., member 6b, is provided in the close-up of FIG. 2d. Notethat the members, when initially constructed, are slightly taperedinward. This is a function of their being injection molded, since thistapering enables the members to more easily be removed from therespective mold. Tapering also improves the strength of the members.

The inner stent frame is also preferably constructed with a view towardseventually covering the stent frame with DACRON fabric and bonding thestent frame to the fabric. To facilitate bonding of the stent frame tothe fabric, energy directors 7a and 7b are provided at the bottom of thestent frame. These directors will be used to attract ultrasonic energy,causing the thermoplastic at this specific location to melt, and bondthe fabric to the stent frame. The energy directors 7a and 7b arepreferably separated by notch 7c as shown. This notch is designed toconsume the fabric seam of the stent sock (illustrated in FIG. 4a) onceit is placed over the inner stent frame.

As illustrated, the annular base 4 of the inner stent frame ispreferably tapered inward at about 5-15 degrees from the vertical. Aswill be discussed further on, the outer stent frame is correspondinglytapered as well. Together, this tapering facilitates nesting between theinner and outer stent frames, which nesting contributes to providing aself-adjusting clamping force over the tissue between the inner andouter stents. Furthermore, the tapering will help bias the valve into aclosed position, which enables the valve to close more easily in lowpressure conditions. Finally, the tapering produces a "jet nozzle"effect which reduces turbulence as blood flows through the valve,leading to a smaller net pressure drop across the valve, resulting inless energy loss to the valve. These concepts will be described in moredetail further on.

Turning now to FIG. 2c, this figure illustrates a top view of the innerstent frame. As illustrated, in the preferred embodiment, threeapproximately equally spaced posts 5a, 5b, 5c protrude from the annularbase, with scalloped edges connecting the posts. However, it should beappreciated that other examples are possible, including where the postsare unequally spaced, and where more or less than three posts extendfrom the base.

Turning now to FIG. 2b, this figure illustrates a side view of the innerstent frame of FIG. 2c. A cross-sectional side view of FIG. 2c waspreviously provided in FIG. 2a. As illustrated, in the preferredembodiment, each post is constructed with two outward-facing members 6aand 6b. Again, however, it should be appreciated that other examples arepossible, such as where each post is constructed With more or less thantwo outward facing members, where only some of the posts are constructedwith outward-facing members, or where the annular base is constructedwith outward-facing members. All these examples are intended to beincluded with the scope of the invention. As will be described in moredetail further on, these members will ultimately be formed into thetissue alignment members which are designed to position the tissue inplace on the inner stent and prevent its movement during valve assembly.

After the inner stent frame is formed, the outward-facing members formedon the stent frame are next processed into tissue alignment members suchas hooks, barbs, or members with mushroom capped ends or the like. FIG.3 illustrates tissue alignment members 6a and 6b configured asmushroom-capped members. Preferably, the members are shaped to havemushroom caps. This is accomplished by directing radiation from anenergy source, such as conventional heat, impulse heat, ultrasonicenergy, or the like, to deform the heads of the members into a mushroomshape. A preferable energy source is ultrasonic energy, since it can beapplied in a controlled manner to form the mushroom heads, but othersources are possible.

Before or after formation of the mushroom heads, the stent frame iscovered with fabric such as DACRON or the like, such that the tissuehooks protrude through the fabric. As mentioned briefly earlier,covering the stent frame accomplishes the purpose of isolatingnon-biological material, such as the thermoplastic of the stent frame,from the body. This helps avoid the problem of thromboembolism, whichoccurs with the use of mechanical valves. It also accomplishes thepurpose of promoting tissue ingrowth into the interstices of the fabric,to further isolate the non-biological material from the body, andintegrate the valve into the heart. Additionally, it accomplishes thepurpose of providing an interface to the tissue clamped between thestents which is gentle, and which helps nourish the tissue and promoteits viability by allowing free passage of blood to the tissue.

To cover the inner stent frame, first, a three-fingered DACRON sock orglove is formed by heat seaming sections of DACRON fabric togetherutilizing either hot wire or ultrasonic techniques. Alternatively, theentire glove can be woven as one piece. The glove is then pulled overthe stent frame, and secured with a heat seam at the base of the glove.The seam and surrounding fabric are then thermally-bonded to the base ofthe stent frame utilizing the energy directors 7a and 7b illustrated inFIG. 2a, in conjunction with ultrasonic energy. Other sources of heatand/or pressure are possible, but ultrasonic energy is preferable, sincethe melt distance, and molten thermoplastic flow into the fabricinterstices, can be accurately controlled and repeated in a productionenvironment with ultrasonic energy.

Turning now to FIG. 4a, additional detail on the stent sock is provided.The three-fingers of the sock, which will fit over the three posts ofthe inner stent frame, are identified with reference numerals 8a, 8b,and 8c. Since the inner stent frame will preferably be manufactured in avariety of sizes, configured depending on the annulus of the heart to befitted, it is desirable to be able to manufacture the stent sock, aswell, in a corresponding variety of sizes. At present, stent socks havebeen produced in sizes ranging from 14 mm-20 mm, although other sizesare possible. It has been found that this range of sizes is acceptablefor use with the inner stent frame sizes of 19-31 mm since the DACRONfabric can easily be stretched to fit over the nominally larger innerstent frame. Moreover, the stent sock is preferably constructed fromknitted DACRON tube similar in weave to implantable large vessel grafts.Both tubular and flat DACRON are possible.

Turning now to FIG. 4b, this figure illustrates a cross-sectionalportion of the stent sock used to cover one of the stent posts,identified with numeral 8a in the figures.

Turning now to the outer stent, additional detail on the outer stentframe is illustrated in FIGS. 5a-5d. A top view of the outer stent frameis illustrated in FIG. 5a. As illustrated, the outer stent framepreferably has a similar construction as the inner stent frame, in thatthe outer stent frame preferably has an annular base 10, and threeequally spaced posts, 9a, 9b, and 9c, protruding from the base along anaxis of the valve in the direction of blood flow, and connected by ascalloped edge. One such edge, identified with reference numeral 9d, isshown in FIG. 5c, connecting posts 9a and 9b.

A side view of the outer stent frame is illustrated in FIG. 5b. Thisfigure illustrates additional aspects of the outer stent frame. Asillustrated, the annular base 10 is preferably constructed with a groove11 around the periphery of the outer stent into which self-adjustingtensioning means such as a garter spring or the like will eventually befitted. In addition, a flange at the bottom of the annular base,identified with reference numeral 12, is provided with an inward taperto facilitate locking the outer stent over the inner stent. Eventually,this flange will be used to lock under the bottom of the annular base ofthe inner stent to ensure a tight fit between the stents.

Another aspect of the outer stent are the windows in the posts.Preferably, each post is configured with a corresponding window, and onesuch window, identified with reference numeral 13a, is shown for post 9ain FIG. 5b. As shown, the window generally defines a contour in thecorresponding post, in this instance post 9b, of the outer stent frame,and is surrounded by a member 13c which gives the shape of the post.Preferably, one such window is contained in all the posts of the outerstent frame, although examples are possible where not all the posts areconstructed with windows. As will be discussed in more detail furtheron, the window is designed to facilitate nesting between the inner andouter stents. When the outer stent is eventually placed in a closemating position with the inner stent, the posts of the outer stent arepreferably situated so as to coincide with the posts of the inner stent.To facilitate nesting, the windows should be large enough to accommodatethe posts of the inner stent, and should generally follow the samecontours as the inner stent posts. During valve assembly, as will bediscussed in detail further on, this nesting will provide aself-adjusting clamping force on the tissue between the stent posts.

A further aspect of the outer stent frame is window extension 13b,illustrated in FIG. 5b, which extends through the annular base of theouter stent. As shown, the window extension extends from the window 13aand through the portion of the annular base below the window.Preferably, one such extension is contained in every post of the outerstent, although other examples are possible, such as where only some ofthe posts contain window extensions, or where the window extensions arereplaced by slots which split the annular base at positions along theannular base below the posts. As will be discussed in more detailfarther on, these extensions or slots enable the outer stent to bespread open so that it can be easily fitted over the inner stent withoutdamaging the tissue during the valve assembly process.

Further aspects of the outer stent frame are illustrated in FIG. 5c,which is a cross-sectional view of the illustration in FIG. 5a. Asillustrated in FIG. 5c, post 9a of the other stent frame is preferablycomprised of two segments 14a and 14b. The bottom segment 14b ispreferably tapered inward at an angle of about 5°-15° from the centraldimension, whereas the top segment 14a, is preferably straight.Preferably, each of the posts of the outer stent frame are configured inlike manner.

This tapering configures the outer stent to fit closely with the innerstent, which, as discussed previously, is similarly tapered. Moreover,this tapering serves additional purposes, including producing the jetnozzle effect, and biasing the valve into a closed position.

A further aspect of the outer stents are the energy directors 15. Theseserve the same purpose as the energy directors of the inner stent: Theyserve to attract energy, preferably ultrasonic energy, enabling thethermoplastic in the immediate vicinity of the director to melt in acontrolled manner.

Further detail on the energy directors is provided in FIG. 5d. Asillustrated, the energy directors extend around the periphery of theannular base, and consist of thermoplastic formed into sharp corners.One such director, identified with numeral 15a, extends around the topof the annular base, while the other, identified with reference numeral15b, extends around the bottom of the annular base. The groove 11 in theannular base, previously described, is situated between the twodirectors.

As with the inner stent frame, the outer stent frame is preferablyinjection molded out of a thermoplastic such as DELRIN or the like, andthen covered with a DACRON stent sock, which is then closed with a heatseam at the base of the stent. Then, the sock is thermally-bonded to thestent upon the application of heat and pressure, which is preferablyapplied through the application of ultrasonic energy. The placement ofthe energy directors is such that the DACRON fabric will be bonded tothe outer stent frame along two concentric seams on either side of thenotch.

Other variants of the outer stent frame are possible. In one variant,the outer stent frame is a composite structure, whereby the posts of thestent frame are manufactured using a spring alloy metal such as MP 35N,ELGILOY, 17-7PH Stainless, or the like, while the annular base of thestent frame will continue to be made from thermoplastic. The benefits ofthis composite structure are that the overall mass of the outer stentposts is reduced, and in addition, the manufacturability of the outerstent frame may be improved, and provide even greater control of theouter stent clamping.

It should be appreciated that the outer stent frame can be integratedwith other components before it is covered with the stent sock. In thepreferred embodiment, for example, the outer stent frame is integratedwith a elastomeric collar and self-adjusting tensioning means before itis covered with the stent sock. Together, these components define theouter stent identified with numeral 1 in FIG. 1. Preferably, theself-adjusting tensioning means is a garter spring, which floats in theouter stent groove, but it can be any other helically wound wire or thelike. The spring is preferably made out of a material such as MP-35N, acobalt nickel-chromium and molybdenum alloy, or the like, and othermaterials are possible provided that the material has goodbio-compatibility, has high strength, and can produce a known, constantand evenly distributed clamping force. For example, elastomer rings arepossible since they meet these criteria. Additional detail on the garterspring is provided in FIGS. 5e-5h. The spring is advantageously coiledat 7 mils/coil, with a diameter of about 38 mils for each coil. Thespring is formed out of a wire coil, where the spacing between the coilsis advantageously equal to the diameter of the wire. As illustrated inFIG. 5h, the ends of the spring are advantageously connected simply byscrewing them together. The length of the spring should be such as toaccommodate the outer diameter of the outer stent. It should beappreciated that these dimensions can change with valve size.

The outer stent is assembled by placing the garter spring or the likeinto the groove 11 in the annular base of the stent frame, followed byplacing the elastomeric ring around the garter spring. The elastomericring is preferably made of silicon or the like, although other examplesare possible, provided that the material used is flexible, resilient,and has relatively high strength. Then, the DACRON stent sock isthermal-bonded to the thermoplastic frame in the manner describedpreviously. The result is an integrated structure which is flexibleenough to be spread open wide enough to fit easily over the inner stent,while also being capable of retracting automatically to apply aself-adjusting clamping force to the tissue between the stents. Theself-adjusting aspect of the clamping force is beneficial; it enablesthe tissue to be clamped without slippage even though the thickness ofthe tissue used may vary, depending on the individual patient, and inaddition, despite irregularities in the tissue itself which may causethe thickness to vary within the piece of tissue.

The elastomeric ring, when covered with the DACRON fabric, will serve asa sewing ring in the completed valve assembly. Specifically, this ringwill be the vehicle for sewing the assembled valve into the annulus. Thegarter spring and elastomeric ring cooperatively interact, in that ifthe garter spring breaks for any reason, the integrity of the valve willbe maintained by the elastomeric ring, which will act as back-up to thespring. The elastomeric ring will also help prevent the garter springfrom slipping out of its groove. As a result, the valve will retain itsshape, retaining the inner stent, and will not catastrophically failunder these circumstances.

Turning now to FIGS. 6a-6d, these figures illustrate the two stentsafter the outer stent has been placed over the inner stent, to beconcentric with it, with the posts of the two stents aligned. Asillustrated, the configuration of the stents is such that the posts ofthe inner stent nest into the corresponding windows of the posts of theouter stent. This nesting does not, in fact, completely occur in theassembled valve however, since in the assembled valve, tissue will beplaced between the posts, preventing complete nesting. In the assembledvalve, the posts will attempt to nest with each other, but will beprevented from completely doing so by the tissue. This tendency towardsnesting is beneficial, since it will provide a self-adjusting clampingforce on the tissue between the stent posts, leading to less slippage,and therefore better matching of the co-aptive edges of the tissueleaflets. Another benefit is that the tissue between the stents will bemore uniformly clamped in that the tissue between the posts will besecurely clamped as well as the tissue between the annular bases.

Uniform clamping is beneficial for several reasons. First, it furtherreduces stress which may otherwise concentrate at the tissue alignmentmembers. Second, if the tissue were to be formed by suturing a number ofsmaller pieces of tissue together, instead of just a single piece oftissue, uniform clamping helps relieve stress from these sutures aswell. The result is a prolongation of the valve life.

For illustrative purposes, in FIGS. 6a-6d, the nesting between innerstent post 5a and outer stent post 9a is shown. It should beappreciated, however, that in the preferred embodiment, each post of theinner frame will nest with a corresponding post of the outer frame. Alsoshown, in cross section, is garter spring 16 which is wrapped around theannular base of the outer stent frame. Finally, elastomeric collar 17 ofthe integrated sewing ring is also shown in cross-section.

As illustrated, the tapering of the annular bases of the inner and outerstent posts appropriately positions the windows of the outer stent postswith respect to the inner stent posts to facilitate nesting. In fact,the taper is such that the diameter of the inward-facing surface of thetop of the posts of the outer stent is approximately the same as thediameter of the outward-facing surface of the top of the posts of theinner stent. This condition ensures that this nesting takes place. Thisnesting provides an inherent self-adjusting clamping force which will beused to clamp the tissue uniformly between the posts.

Several physical dimensions are critical to the proper functioning ofthe valve. These dimensions are identified with reference numerals 18,19, and 20 in FIG. 6c, and numeral 100 in FIG. 6b.

With respect to the dimension identified with numeral 18, this dimensionis the nominal distance between the mated stents along a channel whichextends down the sides and along the bottoms of the stents. It has beenfound that for pericardial tissue, the dimension is preferably about0.020 inches, in order to accommodate the thickness of the tissue andthe thicknesses of the DACRON fabric coverings, although for othertissue types such as fascia lata, other dimensions may be preferable.

The distance is only nominally 0.20 inches, however, since in theassembled valve, the actual distance will depend on the thickness of theactual tissue used. The self-adjusting tensioning means will cause thisdistance to expand or contract, in response to the specific tissuethickness, in order to generate a self-adjusting clamping force on thetissue.

As discussed earlier, the benefit of the self-adjusting attribute of theclamping force is less slippage and better stress distribution. Anotherbenefit is that the tissue will be squeezed into the interstices of theDACRON fabric covering the stents. This results in even less slippage ofthe tissue.

Turning to the next critical dimension, identified with numeral 19, thisdimension is the clearance between the bottom of the annular base of theinner stent and the top surface of the flange of the outer stent. Asindicated, this dimension helps define a continuation of the samechannel, discussed earlier, defined by dimension 18. As with dimension18, for use with pericardial tissue, this dimension is preferablynominally about 0.020 inches, although other dimensions may be moreappropriate for other tissues. It should be noted that the tissue in theassembled valve will normally extend down to point 21, at which point,the pre-cut edge of the tissue will terminate.

Turning to the next critical dimension, identified with numeral 20, thisdimension is the clearance between the bottom of the window in the outerstent post and the top of the corresponding inner stent post. Thisdimension should be large enough to accommodate double the thickness ofthe DACRON fabric that is used to cover the stents, but does not have toaccommodate the thickness of the tissue, since the tissue does not passbetween the bottom of the window and the top of the inner stent post.However, since a seam in the fabric typically runs along the upperscalloped edge of the inner stent, this dimension should also be largeenough to accommodate this seam.

Turning next to dimension 100 in FIG. 6b, this dimension is theclearance between the inner stent post and the struts which form thewindow in the outer stent post. This dimension is typically 20 mils,but, as with the dimension identified with numeral 20, can vary withvalve size, and only needs to be large enough to accommodate double thethickness of the DACRON fabric used to cover the stents.

Finally, other dimensions are identified with the letters A-K in FIGS.6b-6c. These dimensions are proportionate to the size of the annulus tobe fitted with the valve. The following table shows the preferablerelationship between these dimensions (in inches) and a variety ofpossible sizes of the annulus to be fitted:

                                      TABLE I                                     __________________________________________________________________________    ANNULUS                                                                       SIZE   A   B   C   D   E   F   G   H   J   K                                  __________________________________________________________________________    19 mm  .748                                                                              .90 .540                                                                              .352                                                                              .415                                                                              .500                                                                              .025                                                                              .020                                                                              .043                                                                              .055                               21 mm  .827                                                                              .98 .594                                                                              .370                                                                              .455                                                                              .545                                                                              .027                                                                              .023                                                                              .045                                                                              .058                               23 mm  .905                                                                              1.06                                                                              .651                                                                              .405                                                                              .500                                                                              .595                                                                              .030                                                                              .025                                                                              .050                                                                              .060                               25 mm  .984                                                                              1.14                                                                              .708                                                                              .442                                                                              .545                                                                              .645                                                                              .037                                                                              .030                                                                              .055                                                                              .063                               27 mm  1.063                                                                             1.22                                                                              .764                                                                              .477                                                                              .585                                                                              .695                                                                              .040                                                                              .035                                                                              .060                                                                              .065                               29 mm  1.142                                                                             1.30                                                                              .821                                                                              .512                                                                              .630                                                                              .745                                                                              .045                                                                              .040                                                                              .065                                                                              .068                               31 mm  1.220                                                                             1.38                                                                              .877                                                                              .547                                                                              .675                                                                              .795                                                                              .050                                                                              .045                                                                              .070                                                                              .070                               TOL.   -.040                                                                             +.040                                                                             -.005                                                                             +.005                                                                             +.005                                                                             +.005                                                                             -.003                                                                             +.002                                                                             +.005                                                                             -.005                              __________________________________________________________________________

It should be emphasized that other valves sizes are possible such asvalves configured for young children, where the annulus size might be assmall as 14 mm.

The dimensions in Table I above have proven to be acceptable inpractice. In other words, valves formed from components fabricated withthese dimensions have proven to operate successfully.

These dimensions should, however, be as close as possible to dimensionsdetermined from a theoretical ideal. In the theoretical ideal, thesedimensions should preferably stand in certain relationships to eachother, which relationships can be mathematically defined by two ratios.The first ratio can be expressed as follows:

    ((π/3) *(C-K))/(C-G)

The values of dimensions C, K, and G should be such that the ratio aboveis close to 1. Intuitively, this ratio is the ratio between the lengthof the tissue in a cusp of the assembled valve which is free to move, tothe length of tissue required for the valve to close. If the ratio isless than one, the valve will not completely close, although it willclose responsively. If the ratio is greater than one, this means excesstissue will be available with risk of prolapse, stress lines, excessivecentral droop under load, and uneven distribution of tension throughoutthe cusp.

This ratio is further illustrated with the aid of FIG. 6e, which shows atop view of the assembled valve. These dimensions C, G, and K, used toform the ratio, are also illustrated.

Focusing for the movement on a single cusp, the length of tissuerequired for the valve to close will be given by twice the inside radiusminus the width of the post tops, which can be expressed as C-G. Thetissue that is free to move, by contrast, is 1/3 of the circumference ofthe cylinder formed by the tissue, with an adjustment made for thetissue situated behind the top of the posts of the inner stent, which,in fact, is not free to move. This value can be expressed as π/3 *(C-K).

It should be appreciated that the preferred value of this ratio dependson the type of tissue used in the valve, taking account of any observedor predicted shrinkage, or stretching. The ratio should be variedaccording to the long term behavior of the tissue in situ. For example,fascia lata stretches more than pericardium. Hence, for fascia lata, thepreferred value of this ratio should be different from that forpericardium to account for this stretching. It may also vary with thematerial used to form the stents. In addition, since bovine pericardiumhas been observed to stretch quite a bit, a valve designed for use withbovine pericardium should be designed with a ratio smaller than 1. Thisstretching may not occur with viable tissue, such as human pericardium,which may even shrink. Hence, with human pericardium, the ratio may evenbe greater than one. Moreover, it may be advantageous to build slightredundancy into the valve. This can be accomplished by designing a valveconfigured for a ratio slightly greater than one. Such a valve wouldmodel the native valve, which is configured by nature with slightredundancy.

The second ratio can be expressed as follows:

    2 * (D-J)/C

The values of the dimensions C, D, and J should also be such that thesecond ratio is as close as possible to 1. Intuitively, this ratiodefines the geometry of a vertical centerline profile of a cusp when thevalve is in a closed position, without any pressure being exerted on thevalve. A spherical geometry for the centerline profile is preferred,since geometries other than this will yield a valve which is too tall ortoo short. If the valve is too short, even though it may becharacterized as being low profile, the valve now has less stent profileto distribute stress to. If the valve is too tall, it will have all ofthe attendant problems associated with that characteristic.

This ratio is the ratio between the height of the tissue in a cusp whichis free to move, which can be expressed as D-J, to the inside radius ofthe valve, which can be expressed as C/2. If this ratio is equal to 1,the centerline profile of the cusp will approximate a spherical shape,whereas if the ratio is greater or less than one, the centerline profilewill approximate an elliptical shape. If the ratio is greater than one,the valve may be too short for adequate stress distribution, while ifthe ratio is less than one, the valve may be too tall. A spherical shapeyields a valve which provides adequate stress distribution, whileavoiding the problems associated with a too tall valve. This ratio canbe further explained using FIGS. 6f-6g. FIG. 6f illustrates the geometryof the centerline profiles for the valve, 71, 72, 73, where the ratiois, respectively, less than 1, equal to 1, and greater than 1. As shown,only the profile where the ratio is equal to 1 yields a sphericalgeometry. FIG. 6g is similar to FIG. 6f, except that here, the geometryof the centerline profile is shown in three dimensions. The geometrieswhen the ratio is less than 1, equal to 1, and greater than 1 areidentified, respectively, with reference numerals 71', 72', and 73'.

The practical dimensions of Table I are substantially close to thetheoretical ideal. The value of these first ratio, computed using thesedimensions, is about 0.997 for all valve sizes listed in the table,while the value of the second ratio, computed using these dimensions, isabout 1.081, again, for all valve sizes listed in the table.

Turning to FIG. 6d, this figures illustrates a cross-sectional view ofboth the inner and outer stents, the inner stent on the left, and theouter stent on the right. Turning to the inner stent, the DACRON sock isadvantageously seamed along the top 74, and along the bottom. Only seam75, however, in this example, is bonded to the stent frame usingultrasonic energy or the like. Turning to the outer stent, the DACRONsock covering this stent is advantageously seamed along the top 76 andthe bottom 78. Again, however, in this example, only the bottom seam 78is bonded to the stent frame. Moreover, in this example, the sock isalso bonded to the frame along perimeter 77, just above the sewing ring,but the sock is not seamed there.

Turning now to the tissue 2 in FIG. 1, this tissue is preferablyautogenous tissue, such as pericardial tissue, but it may also be fascialata, rectus fascia (or sheath), or vein tissue. These tissue sourcesare all relatively flimsy and difficult to handle. This is because thistissue once harvested will have a thickness of about 10-12 mils. Bycomparison, bovine pericardium is about 15-20 mils thick. Therefore, aswill be described in more detail further on, after the tissue isharvested, the tissue is usually quick-fixed by dipping it in 0.6%glutaraldehyde solution. This serves to toughen it, and make it easierto handle.

In addition, other tissue sources besides autogenous tissue arepossible, such as bovine pericardium or other xenograft tissue or thelike. Further, homograft tissue is possible. These tissues could bepre-cut by the valve builder or valve manufacturer outside the operatingroom, and then stored via conventional methods. If these other tissuesources are used, however, the critical dimensions, identified withnumerals 18, 19, and 20 in FIG. 6c, may need to be adjusted accordinglyso that this tissue, which is generally thicker than the preferredtissue sources, can be accommodated.

It should be appreciated that in the assembled valve, the tendencytowards nesting of the posts ensures that the tissue situated betweenthe stent posts and along the scalloped edge between the posts will besecurely and uniformly clamped. Moreover it should also be appreciatedthat the tissue situated between the annular bases of the stent willalso be securely and uniformly clamped between the stents by the actionof the garter spring. Together, this clamping helps ensure that stresswill be distributed more uniformly throughout the valve, compared to theuse of non-clamping means to secure the tissue, or compared to clampingconcentrated just along the annular bases. In the former case,mechanical fixation points will be created at which stress will beconcentrated. In the latter case, stress will be concentrated at thetissue along the annular bases. It should be appreciated, moreover, thatdue to this clamping, the tissue alignment members, after valveassembly, will not constitute mechanical fixation points. Instead, theirprimary role will be limited to tissue alignment during valve assembly.This is important, since, as discussed above, stress tends toconcentrate at mechanical fixation points. Clamping, by contrast, helpsmaintain uniform stress distribution, and extend valve durability.

Turning now to a method of assembling the valve, the valve is capable ofbeing assembled in the operating room from one or more preassembled,sterile, and disposable kits. A first kit, a tissue harvesting andannulus sizing kit, is not dependent on the size of the annulus beingfitted, and provides means to harvest a tissue rectangle which is largeenough to be used with all size valves, means to clean and fix thetissue, and also means to size the annulus. Alternatively, a separatekit could be provided with means to clean and fix the tissue. Thisseparate kit could have applications in separate surgical proceduressuch as repair of native valves. When these steps are accomplished, asecond kit comes into play.

The second kit is dependent on the size of the annulus being fitted. Itprovides means to cut the tissue rectangle into the appropriate patternand size required, it provides the size-specific inner and outer stents,and it also provides means to assemble the components and tissuetogether to arrive at the assembled valve, adapters for mounting theassembled valve in a tester to test the valve before implantation, and aholder to hold the valve during implantation. The tester itself couldalso be provided in this kit, instead of just the adapters, oralternatively, the tester could already be provided in the operatingroom.

An example of a tissue preparation and annulus sizing kit is illustratedin FIG. 7a. Different kits will be provided for the atrioventricularvalve positions (the mitral and tricuspid valves), and for theaortic/pulmonary valve positions. The particular example illustrated inFIG. 7a is a kit for an atrial/ventricular valve. The components in thiskit will now be described, and the differences between this kit and kitsfor aortic/pulmonary valves will be noted.

Tissue template 24 is a rough sizing template, which the surgeonutilizes to ensure that an adequate amount of tissue is harvested,whatever the ultimate valve size turns out to be. To accomplish this,the surgeon will also utilize universal handle 23. First, the surgeonwill screw the threaded end of the universal handle into the template,place the template over the tissue to be harvested, and then, withscissors or the like, cut around the outline of the template to providea rough tissue rectangle. Alternatively, the surgeon may simply placefour small sutures into the tissue at the corners of the template,remove the template, and then cut out the tissue rectangle. At present,the template is preferably 4 in. by 2 in. in area, and is made from aclear bio-compatible plastic such as polysulfone.

Additional detail on the rough sizing template is provided in FIGS.7e-7f, in which like elements are referred to with like referencenumerals. FIG. 7e provides a top view of the template, which isapproximately 4 by 2 inches in area, and is configured with hollow areas52a and 52b, and solid frame 51a, with central member 51b extending fromthe top of the frame to the bottom, separating the two hollow areas. Athreaded hole 53 is also provided to connect with the universal handle.A side view of the template is provided in FIG. 7f.

It should be appreciated that alternatives to the above-describedtemplate are possible for use in harvesting the tissue. A soft andflexible template, for example, could be utilized. This template couldbe adhered to the tissue temporarily while the tissue rectangle is cutout. Modified forceps are also possible which can be used to guide thesurgeon's scalpel. Optical or lighted guides are also possible, whichproject an image of the template onto the surface of the tissue to becut, for use in guiding the surgeon's scalpel.

Turning back to FIG. 7a, a tray is also provided, preferably configuredto provide basins 25, 26, and 27. These basins are approximately 2inches deep. Two will preferably be filled with saline or the like, andthe third, with saline or optionally a fixative solution. The peripheralbasins, 25, 27, are approximately 4 in. by 6 in. One of these basins isconfigured for use as a rinse basin, and the other is also configuredfor use either as a rinse basin, and alternatively as a chemicaltreatment basin. The central basin 26 is approximately 6 inches square,and is configured for use as the central assembly basin. The volumecapacity of the two peripheral basins is preferably 500 cc, and for thecentral basin, 750 cc. These basins will be used as staging andpreparation areas in the course of assembling the valve. Basin 25 willadvantageously be used to clean the tissue, basin 26, for valveassembly, and basin 27, for tissue rinsing or fixing.

Optionally, a separate third kit could be provided with a trayconfigured with a basin containing a fixative solution. This kit wouldbe used only for quick fixing the tissue. In this instance, the thirdbasin 27 in the kit of FIG. 7a would be filled with saline, and used asa rinsing basin, and the separate kit would be used for quick-fixing thetissue.

Turning back to the method of valve assembly, after the rough tissuerectangle has been harvested, basin 25 is utilized to clean the tissueand remove any fatty deposits or the like. Once the tissue has beencleaned, it is inspected to ensure that it will be suitable for use inthe valve.

At this point, the tissue may optionally be "quick-fixed" by dipping ittemporarily in glutaraldehyde or the like. If the surgeon chooses thisoption, basin 27, the secondary tissue preparation area, is utilized forthis purpose. Instead of being filled with saline, however, this basinwould be filled with a chemical solution with a low concentration ofglutaraldehyde or the like. The tissue is then simply dipped in thissolution for about 45 minutes or less, preferably about 10 minutes orless, and most preferably about 5 minutes or less. Alternatively, asdiscussed earlier, a third kit separate from the other two couldoptionally be provided for quick-fixing. This kit could haveapplications in separate surgical procedures such as native valverepair.

This quick-fixing step is desirable since the solution cross linksproteins in the tissue to make the tissue stronger and less pliable.This, in turn, makes the tissue easier to handle, and hence moresuitable for valve construction. Although the biological effects are notcompletely known, it also appears that the quick fix is important to thedurability and long term survival of the tissue, and may aid in thetissue's transition to a leaflet material. In other words, the abilityof the body to nourish and maintain the long-term viability of thetissue may be enhanced by the quick fix.

It should be noted that the function of the glutaraldehyde is differenthere than for prior art tissue valves utilizing bovine or porcine tissueor the like. With these tissues, glutaraldehyde treatment was importantfor attenuating the antigenicity of the tissue in a treatment processwhich typically requires 2-4 weeks, and increasing the inherent strengthof the tissue, while here, the tissue is preferably autogenous tissue,which has no significant antigenicity. Therefore, the beneficial aspectsof the treatment are different. Here, it appears that the solutionselectively kills surface portions of the tissue graft, and that thisselective killing may promote long-term viability of the tissue. Also,the time to perform the process is much shorter. As mentionedpreviously, the autogenous tissue should be dipped into the solution byno more than about 45 minutes, preferably by no more than about 10minutes, and most preferably by no more than about 5 minutes.

Besides glutaraldehyde, it should be appreciated that other chemicalcross-linking agents are possible for use in quick-fixing the tissue,including or in combination, formaldehyde, glycerin, glycerol, or thelike.

Turning back to the valve assembly, at this point, the surgeon orassistant is ready to measure the size of the annulus to be fitted. Thisis where the obturators 22a-22e come into play in conjunction with theuniversal handle 23.

The surgeon or assistant will simply screw the threaded end of theuniversal handle into one of the obturators, and then push the obturatorinto the annulus. The surgeon or assistant will successively performthis step with different obturators from the group 22a-22e until thatobturator is determined which will yield the closest fit. Note that inthe example, five obturators are provided. It should be appreciated,however, that other examples are possible, including examples where moreor less than five obturators are provided.

It should be appreciated also that a variety of sizes of obturators arepossible. For replacement of the mitral valve, an atrioventricularvalve, it is advantageous to provide a set of obturators with diametersof 31, 29, 27, 25, and 23 mm. It should be appreciated that differentsizes, and numbers of obturators may be needed for replacement ofaortic/pulmonary valves. For the aortic valve, it is advantageous toprovide a set of obturators with diameters of 19, 21, 23, 25, and 29 mm.For replacement of valves in young children, it is advantageous toprovide obturators with smaller diameters, i.e., as small as 14 mm.

It may also be necessary to vary the universal handle depending on thevalve type to be replaced. Specifically, the handle is preferablystraight for use in sizing the aortic valve, but angled at about 30degrees for sizing the mitral valve. In either case, whatever angle thehandle is initially set at, the handle should be provided with a meansto slightly deviate from this angle during use in the operating room.

Turning to FIGS. 7b-7c, and FIG. 7g, these figures provide additionaldetail regarding the universal handle as it is configured for use withthe obturators. FIG. 7b illustrates the preferred handle as configuredfor the aortic valve, while FIG. 7c illustrate the same for the mitralvalve.

Turning to FIG. 7b, the preferred handle 47 for the aortic valve ispreferably straight, although means, such as malleable section numeral47c, configured to couple sections 47a and 47b together should beprovided to enable the handle to deviate slightly from this angle. Apreferred configuration for obturator 48 is also illustrated. Asillustrated, the preferred obturator is configured as a spoked wheel.

Turning to FIG. 7c, the preferred handle for the mitral valve isillustrated. As indicated, this handle is preferably angled at about30°, although again, means such as malleable section 47c, used to couplesections 47a and 47b together, should also be provided so that thehandle can be deviated from this angle slightly. FIG. 7d illustrates, ingreater detail, the preferred configuration for obturator 48.

It is desirable to configure a universal handle that can be used withboth valve types. FIG. 7g illustrates such a universal handle. Asillustrated, the holder comprises plastic rod 47a connected by malleablewire 47c to shorter plastic rod 47b. The shorter plastic rod ispreferably threaded at one end 47d in the manner described previously.The rod 47a is advantageously 6 in. long with a diameter of 0.25 in.,while the shorter rod 47b is advantageously 2.0 in. long, with adiameter of 0.25 in. The malleable wire advantageously has a diameter of0.05 in., and is configured to allow the shorter section 47b to pivotabout pivot point 50, by at least about 30 degrees. FIG. 7g illustratesin phantom, the shorter section once pivoted by about 30 degrees infirst one direction, which portion is identified with reference numeral47b(1), and then about 30 degrees in the opposite direction, whichportion is identified with reference numeral 47b(2). It should beappreciated that the universal handle of FIG. 7c is preferablyconfigured to be threaded into the obturator from the opposite side thanthat illustrated in FIG. 7b.

Turning back to valve assembly, at this point, the tissue has beenprepared and the annulus sized. The obturators, tissue template, anduniversal handle are no longer needed, and they may simply be disposedof. Tray 31, however, is kept, since basin 26 is still needed as aconstruction area for assembly of the valve.

The surgeon or assistant next selects a size-specific aortic or mitralstent kit, which contains all the components needed to complete theassembly of the valve. Again, for the mitral valve, size-specific stentkits configured for five annulus sizes, 23, 25, 27, 29, and 31 mm, aredesirable, while for the aortic kit, 19, 21, 23, 25, 27, and 29 mm kitsare desirable. It should be appreciated that other size kits arepossible, i.e., a 14 mm kit for young children.

The components in the size specific stent kit are illustrated in FIG.8a, in which, compared to earlier figures, like elements are referred towith like reference numerals. As indicated, this kit contains tray 49configured to hold inner stent 3 (already covered by and thermal-bondedto its corresponding DACRON cover), outer stent 1 (already integratedwith a garter spring and elastomeric ring and also covered andthermal-bonded to its corresponding DACRON cover), size-specific tissuecutting tools 28, assembly mandrel 29, outer stent spreading tools 30,adapters for mounting the valve in a valve tester (not shown), andoptionally a valve holder (not shown) for use by the surgeon to hold thevalve during implantation.

Turning back to valve assembly, after selecting the appropriate stentkit, the surgeon or assistant next further cuts the tissue rectangle toobtain the exact geometry required for valve construction. To accomplishthis, the surgeon or assistant utilizes tissue cutting tools 28.

At present, these tools comprise tissue cutting die 31, and base 58. Anembodiment of the tissue cutting die is illustrated in FIGS. 8d-8f; asecond embodiment is illustrated in FIGS. 8g-8i. The base 58 isgenerally illustrated in FIG. 8c, and with more detail, in FIGS. 8j-8k.

Turning to the die first, this die comprises a razor-sharpened and honedblade 33 embedded in thermoplastic frame 54 comprised of plastic blades55 and 56. Also included are a plurality of ferrule pairs 34a, 34b, 34c,and 34d, which are also embedded in the thermoplastic.

The objective of this step is to process the roughly-sized tissuerectangle into the specific geometry, illustrated in FIG. 8l, needed forconstruction of the valve. To perform this step, the surgeon orassistant simply places the rough tissue triangle on the base 58,locates the die over the tissue, and presses down on the die in asimilar manner to a cookie cutter to cut out the corresponding tissue 2.

The blade 33 is typically sharpened to about 100-300 Angstroms (bycontrast, a surgeon's scalpel is typically only sharpened to about 300Angstroms), and preferably, to about 150-200 Angstroms, and extendsabout 35 mils above the upper surface of the thermoplastic frame 54.Therefore, only a small amount of pressure on the die will be requiredto cut out the tissue. Other methods or tools, i.e., a screw orhand-held clamp, which predetermine and limit the cutting force anddepth, may be used to cut the tissue.

The blade is preferably shaped to have the same outline as the desiredtissue 2 illustrated in FIG. 8l. In addition, the ferrule pairs 34a-34dare preferably positioned and sized to cut appropriately positionedholes in the tissue 2, which will ultimately be registered with thetissue alignment members extending from the inner stent. At present, theferrules are advantageously approximately 0.025 in. in diameter, and theblade is constructed from Sandvik 6C27 or equivalent and the ferrulesare constructed out of 316 or 303 stainless steel, but it should beappreciated that other materials are possible, including thermoplastics,composites, ceramics, or combinations of the above.

In FIG. 8d, four pairs of ferrules are shown in the tissue cutting die.FIG. 8l shows the resulting holes which are cut into the tissue. Itshould be appreciated, however, that other hole configurations arepossible. The purpose of the holes is to enable the tissue to beprecisely positioned with respect to the inner stent during valveassembly, and prevent circumferential movement of the tissue, ormovement of the tissue up or down, during the valve assembly process. Asmentioned previously, improper placement, or circumferential or othermovement of the tissue during the valve assembly process can lead toprolapse, which can induce undue strain on the valve, and leakage of thevalve. Specifically, with respect to FIG. 8l, if section 59a of thetissue were to be stretched too tightly during the valve assemblyprocess, the co-aptive edge of the leaflet formed by this section maynot properly join with the co-aptive edges of the other two leaflets,but will instead, strike these leaflets below their co-aptive edges. Theresult is that the co-aptive edges of the leaflets formed by sections59b and 59c will not be able to transmit stress to the co-aptive edge ofleaflet 59a, with the result that leaflets 59b and 59c will be subjectedto undue stress. Moreover, leaflet 59a will be subjected to undue stressas well. This is because leakage may be induced at the center of thevalve, and this leakage will exert strain on leaflet 59a while the valveis in a closed position. The registry of the holes with the tissuealignment member helps prevent prolapse, and therefore eliminate thisstress and leakage problem.

Therefore, other configurations of holes and corresponding tissuealignment members are possible, as long as the above objective isachieved, including configurations where more than two members areconfigured on each stent post, or where members are also distributedaround the annular base of the stent. However, in all theseconfigurations, the number of holes and corresponding members should notbe too great since too large a number of holes may unacceptably slowdown the assembly process as the surgeon or assistant attempts toregister all the holes with the corresponding tissue alignment members.By contrast, the valve described in the '483 patent employs a total of27 pins and studs, which must be registered with corresponding holes orslots in the outer stent. This configuration makes it difficult orimpossible to assemble this valve in the limited time available in theoperating room.

Moreover, the number of members should not be too large so as to createmechanical fixation points in the assembled valve. If too large a numberof members is utilized, the numbers may begin to play such a role in theassembled valve. Specifically, the tissue alignment members are designedto only position the tissue during valve assembly, and their primaryrole ceases after valve assembly. This is because in the assembledvalve, as stated previously, the clamping force generated by the stentssubstantially holds the tissue in place to more uniformly distributestress. If the tissue were to be held in place in any significant degreeby the members after assembly, then the stress would be focused at thesemechanical fixation points, which could lead to premature tearing of thevalve.

Finally, in all configurations, the members should not be configured toconnect to the outer stent, or to project into corresponding holes inthe outer stent which register with the members. This is why the outerstent is not configured to have any holes which register with themembers. If the members connected to or registered somehow with theouter stent, then the members could begin to play a fixation role in thecompleted valve, and further, mechanical fixation of the two stentscould impede the flexible nature of the stents.

As discussed previously, the stents of the subject invention preferablyhave flexible frames made of thermoplastic. The flexible nature of thestents further contributes to the ability of the assembled valve towithstand stress. If pins or studs were used to connect one stent toanother, then for one stent to flex, it would have to pull the otherstent along with it. Consequently, the flexing of the stents would beimpeded, which would form even more stress on the tissue and pins.

A preferred configuration is about nine members or less distributedaround the inner stent. Preferably, the members do not extend into holesor slots in the outer stent. It should be appreciated, however, for thereasons stated earlier, that other configurations are possible.

Turning to FIGS. 8d-8f, the die is configured with two plastic blocks,identified with numerals 55 and 56. These blocks are preferablyconstructed from a clear or translucent plastic, biomedical gradematerial. The ferrules are embedded in block 56. Block 55, in turn, isembedded within block 56. Blade 33 is embedded at the interface betweenthe two blocks. Block 56 is also configured with hollow regions 57a,57b, and 57c, within it, to provide enhanced visibility of the tissuebeing cut. A side view of the die of FIG. 8d is provided in FIG. 8e,while FIG. 8f provides additional detail on the blade and ferrules. Inthis embodiment, the blade is preferably razor-sharpened to about150-200 Angstrom, extends 35 mils above the blocks, and is parallel tothe surface of the block within a tolerance of 1 mil. The ferrules alsopreferably extend 35 mils above the blocks, and are parallel withrespect to the surface of the blade within a tolerance of 1 mil.

Turning, for the moment, to the base to be used in conjunction with thedie, as illustrated in FIG. 8c, the base actually comprises severalcomponents, including block 77, cutting pad 78, outline 79, and guidepins 51a-51d.

The block 77 is preferably made of a material that is clear ortranslucent, so that, if desired, it could be back-lit. Moreover, thematerial should be such that the base may be disposed of or recycled.

The cutting pad 78 is preferably a thin, i.e., 0.025 inch or less, sheetof TEFLON or the like, and is configured to provide an appropriateamount of resiliency against the razor sharp blade of the die. Thethickness of the pad is determined by the extent to which blade 33extends above the upper surface of the cutting die 36 and by thethickness of the tissue used. In the example discussed earlier, theblade extension is 35 mils. and human pericardial tissue may be about 10mils thick. The thickness of the pad should be the difference, i.e., 25mils, in this example. The cutting pad functions to limit the bladepenetration into the tissue and the base on which it is resting.

The cut outline 79 is an outline of the desired tissue piece, and caneither be integrated into the cutting base or cutting pad. This outlineis used to project an outline of the cut pattern through the transcalenttissue so that the valve builder can precisely know which portion of thetissue will be cut, and can thereby avoid any undesirable portions ofthe tissue, including irregularities, adhesions, or areas which maycontain too much or too little collagen.

The guide pins 51a-51d index with holes in the cutting die.

In cooperation with the cutting die 31, the cutting base can be used asfollows. First, the rough tissue rectangle would be placed over thecutting pad until the desired portion of the rectangle is over theoutline on the cutting pad. Then, optionally in cooperation with theguide pins, the cutting die is lowered until the blade in the die cutsthe tissue exactly as in the outline.

FIGS. 8j-8k provide additional detail on the cutting base 58. Comparedwith FIG. 8e, like elements are referenced with like identifyingnumerals in these figures. FIG. 8j is a top view of the base, while FIG.8k is a side view. The block 77 in this example is dimensioned to be 3.5in. by 1.5 in. by 0.25 in. Moreover, the guide pins in this example areconfigured to have a diameter of about 0.125 in., and to have taperedends as shown.

An alternative embodiment of the tissue cutting die 58 is illustrated inFIGS. 8g-8i, in which, compared to FIGS. 8d-8f, like elements arereferenced with like identifying numerals. An important aspect of thisembodiment is that it is configured to cooperatively interact with thecutting base of FIGS. 8j-8k.

In this embodiment, the blade 33, and block 56 are embedded in a secondblock 55 configured to have about the same shape as the block 77 of thecutting base 58. Block 55 is also configured with indexing holes76a-76d, which are adapted to mate with the indexing pins 51a-51d of thecutting base 58. In the particular example illustrated, the holes areconfigured with a diameter of 0.125 in. With this embodiment, the roughtissue is cut by placing it on the cutting pad of the base, and thenlowering the die to cut the tissue with the pins of the base indexingwith the corresponding holes in the block 55 of the die.

The preferred tissue pattern of the precisely cut tissue is illustratedin FIG. 8l. As illustrated, the tissue pattern is a flat conicalgeometry, that is, it is a cone unwrapped onto a flat surface, withleaflet edges 59a, 59b, and 59c formed from a plurality of radiiextending from a free margin.

An important aspect of the pattern is the placement of hole pairs 60a,60b, 60c, and 60d, which are cut into the tissue by ferrules 34a, 34b,34c, and 34d of the tissue cutting die. These holes are small, having adiameter of about 25 mils, so that they will register with the tissuealignment members, 6a and 6b, extending from the inner stent.

Although the body of the members should have a diameter of 25 mils, theheads of these members should have a diameter slightly greater than 25mils, since they are formed by flattening the tips of members 6a, 6b,illustrated in FIG. 2d, which are initially formed with a 25 mildiameter. Consequently, when the precisely cut tissue is wrapped aroundand registered with the inner stent during valve assembly, these holeswill literally be "popped" over the tissue alignment members, andthereafter be prevented from circular, or up or down, movement by themembers. Moreover, these holes are precisely placed so that the tissueused to form each of the leaflets in the assembled valve, identifiedwith numerals 61a, 61b, and 61c in FIG. 8l, respectively, will beuniform. Consequently, the hole pairs should be uniformly radiallyspaced so that the resulting leaflets will be uniformly sized. Also, inFIG. 8l, each of the resulting bottom edges of each leaflet, identifiedwith numerals 62a, 62b, and 62c, should extend radially uniformly.

Variants on the tissue cutting tools are possible. Specifically, theblock could be configured from a range of materials besidesthermoplastic, such as TEFLON. In addition, the blocks 55-56 could beconstructed out of a number of materials, including polycarbonate,polysulfon, nylon, epoxy, or the like, as long as the material isbio-compatible. It is desirable for the blocks to be translucent. Thislatter requirement is so that the surgeon or assistant can moreprecisely align the tissue die over a particular portion of the roughtissue rectangle that the surgeon or assistant believes is moredesirable than others for use in the assembled valve.

Alternatively, instead of using a die, a soft template made of siliconeor the like could be temporarily adhered to the tissue, and then thetissue cut out by following a scalpel along the outline. Alternatively,the tissue could be marked with an FDA-approved dye while the templateis in place, the template would then be removed, and the tissue cut outusing the pattern formed by the dye on the tissue. Other possibilitiesinclude laser based or water jet systems with or without computerassistance, male/female dies, modified forceps to be used withconventional surgical cutting instruments, and optically generatedtemplates projected onto the tissue. Hand held devices, such as modifiedforceps or the like, adapted to close a base and corresponding dietogether to cut the tissue using hand pressure, are possible.

Variants of the tissue configuration to be formed are possible also.Specifically, instead of being configured as the precisely cut patternillustrated in FIG. 8l, the tissue could be configured as three separateprecisely cut pieces, corresponding to the three valve leaflets, whichpieces could then be separately arranged around the inner stent. Apossible problem with this approach may be that it could adverselyaffect the clamping ability of the stents. This is because these threesections will need to overlap slightly at the posts of the inner stent,leading to three seams having twice the thickness of the tissue itself.These seams may interfere with or prevent the clamping of the tissuebetween the seams. Hence, the single piece configuration is preferred.

In the subject valve, the self-adjusting tensioning means provides thecapability of adjusting for tissue irregularities, and hence, couldovercome this problem. The valve described in the '483 patent, on theother hand, utilizes pins and studs to hold the tissue in place in theassembled valve. This approach, however, is very time-consuming toassemble, and leads to undue stress buildup. Hence, the use of theself-adjusting tensioning means is preferred.

Turning back to the valve assembly process, the next step is to positionthe inner stent utilizing assembly mandrel 29. The basin 26 in thepreparation and sizing kit illustrated in FIG. 7a provides a convenientconstruction area for placement of the mandrel.

Turning to FIG. 8b, this figure illustrates the mandrel in more detail.As illustrated, the assembly mandrel comprises two sections, a base 29band a top portion 29a, with an edge 29c along the periphery of the baseat the junction with the top portion. Preferably, the top portion 29a isa replica of the leaflets of the desired valve when placed in a closedposition.

After the mandrel has been positioned, the next step is to place theinner stent over the top of the mandrel until the bottom of the stentrests against the edge 29c. In the course of placing the inner stentover the mandrel, the posts of the inner stent are placed overcorresponding sections 32a, 32b, and 32c within the top portion, 29a, ofthe assembly mandrel. The inner stent is also advantageously indexed tothe mandrel, through the use of appropriately configured detents or thelike, in order to facilitate placement of the inner stent over themandrel.

After the inner stent has been positioned on the mandrel, the cut tissue2 is applied to the inner stent by popping, in succession, the pairedholes in the tissue with the corresponding tissue alignment membersextending from the inner stent posts, and placing the bottom edge 62 ofthe tissue in proximity to the bottom of the annular base of the innerstent. The result is to wrap the tissue around the stent to form atissue configuration in the shape of a cone. The ends of the tissue inthe proximity of the first and last pairs of holes, identified withnumerals 60a and 60d in FIG. 8l, will be popped over the same tissuealignment members, causing this tissue to overlap slightly, andeliminating the need to suture the ends of the tissue together. Althougha small seam of double thickness will be formed, this one seam has beenfound not to interfere with the clamping effect of the stents.

Turning back to valve assembly, once the tissue has been mounted overthe inner stent, it is then smoothed over the mandrel. This smoothingstep acts to configure the tissue into the three valve leaflets, and tofurther position the leaflets into a closed resting position. Eachleaflet is smoothed over the mandrel to eliminate wrinkles, puckers, orother irregularities in the tissue that could preclude a successfulvalve assembly.

At this point, the outer stent spreading tools 30 come into play. Thesetools are illustrated in FIGS. 9a-9d, in which like elements arereferred to with like identifying numerals. The outer stent spreadingtools 30 comprise sleeve 80, top spreading tool 35, and spreading bullet36. All these components are size-specific, and hence provided in thestent kit. The objective of these components is to spread open the outerstent, enabling it to be easily situated over and placed in a closemating position with the inner stent with the tissue clamped in placewithout damaging the tissue.

To accomplish this objective, first, sleeve 80 is placed over thespreading bullet 36, as illustrated in FIG. 9c. As illustrated in FIG.9d, which is a cross-sectional view of the sleeve 80 while situated onthe bullet 36, the sleeve 80 has a tapered cuff portion 80b, whichfacilitates sliding the outer stent over the sleeve. As mentionedpreviously, the outer stent is configured with window extensions, slots,or the like, along the annular base, enabling the stent to be splayedopen. The outer stent is pushed, bottom first, over the top of thespreading bullet. The bullet causes the outer stent to spread open, andthe tapered cuff promotes the sliding of the annular base of the outerstent onto the sleeve 80 until the bottom of the annular base of thestent is resting against ledge 80c of the sleeve.

Next, the spreading tool top 35 comes into play. This top is illustratedin FIG. 9a. As illustrated, the top comprises three blade pairs, 35a,35b, and 35c which pairs extend from, and are about equally spacedaround the periphery of an annular cusp 35d. The objective of the top isto sustainably spread the posts of the outer stent outward. The bladepairs are configured such that the two blades making up one of the pairsare capable of coinciding with the left most and right most strutsmaking up the corresponding post in the outer stent.

Turning to FIG. 9b, the top 35 is then fitted onto the outer stent, thebottom of which is already sustainably splayed upon by the sleeve 80, sothat each pair of blades is aligned with the stents in the correspondingouter stent posts. This causes the posts of the outer stent to spreadopen.

Next, sleeve 80, assembled in conjunction with the top 35 to hold theouter stent open, is removed from the spreading bullet. This assembly isthen placed over the assembly mandril, and then lowered until the outerstent is in position to mate with the inner stent, i.e., the posts arealigned, etc. The action of the sleeve and spreading tool top, insustainably opening the outer stent, ensures there is no contact betweenthe outer stent and the tissue which could result in damage to thetissue. When the outer stent has been appropriately positioned, thesleeve 80 is pulled downwards, causing it to separate from the outerstent, which is restricted from moving downwards also by the innerstent. With the removal of the sleeve, the annular base of the outerstent, through the action of the self-adjusting tensioning means,collapses over the annular base of the inner stent, to clamp that tissuesituated along the annular base of the inner stent.

The outer stent spreading tool sleeve 30c and the inner stent and bothpreferably indexed to the mandrel through a plurality of cooperatingdetentes in the mandrel to aid in alignment of the outer stent over theinner stent. Alternatively, the sleeve and inner stent could be indexedthrough a pin and slot arrangement.

Next, the spreading tool top 35 is pulled off the top of the outerstent, causing it to separate from the outer stent, which is restrictedfrom moving upwards also by the locking flange 12, which by this time,will be in locked position under the base of the inner stent. Thisaction releases the posts of the outer stent, and allows them to retractto mate with the corresponding posts of the inner stent, and securelyclamp the tissue situated behind the posts of the inner stent, and alongthe scalloped edge connecting the posts of the inner stent.

After this step is performed, the valve assembly is completed, and thefinal step, valve testing, can begin.

As stated previously, a significant aspect of the completed assembly isthe enhanced clamping of the tissue provided by the stents, and theelimination of mechanical fixation points between the tissue and thestents. Not only will the tissue which is situated along the annularbases of the stents be clamped securely in place by this arrangement,but the tissue situated at the posts and along the scalloped edgebetween the posts will also be clamped securely in place. Because ofthis enhanced clamping, and elimination of mechanical fixation points,stress will be more uniformly distributed throughout the valve. The longterm durability of the valves is therefore improved.

The clamping along the annular base is provided by the garter spring,while the clamping at the posts and scalloped edge is provided by thenesting of the inner and outer stent posts. Note that after the stentshave been covered with DACRON fabric and after the tissue has beenplaced over the inner stent, complete nesting of the stent posts can nolonger occur. However, the tapering of the outer stent posts towards theinner stent still ensures that a sufficient clamping force will begenerated to hold the tissue in place.

Another significant aspect of the completed assembly is the cessation ofthe primary role of the tissue alignment members after valve assembly.As indicated previously, the primary role of these members is to ensureproper placement of the tissue, and to prevent movement of the tissueduring valve assembly, thereby reducing or eliminating prolapse. In thecompleted assembly, though, it is important that these members not formmechanical fixation points of the tissue to the stents, since stresswould then be concentrated at these points, possibly leading topremature tearing of the tissue at these points, and hence, failure ofthe valve. This objective is accomplished through the enhanced andself-adjusting clamping, which is sufficient to hold the tissue inplace.

Turning now to the testing device, two possible embodiments of thetesting device are illustrated in FIGS. 10a-10c. The purpose of thetesting device is to rapidly test the valve before implantation toensure it is not leaking unacceptably and does not have any othersignificant flaws.

Turning to FIG. 10a, the tester comprises bellows 81, valve adapters 37,calibrated float 40, and clear viewing chamber 39. The bellows arepreferably calibrated, having a known volume and spring rate. Theadapters 37 are used to mount the valve in the tester while preventingleakage around the sewing base. These adapters are size-specific to theparticular valve to be tested, and hence are preferably provided in thesize specific stent kit. The tester itself could, as well, be providedin the kit, or alternatively, could already be available in theoperating room. The clear viewing chamber 39 enables a viewer tovisually observe the valve during testing. The calibrated float 40provides a means to functionally measure leakage or pressuredifferential across the valve.

This tester operates as follows: First, the bellows is used to displacea known volume of saline through the valve. After this is accomplished,the spring rate of the bellows applies a known back pressure to theclosed valve. The calibrated float is calibrated to be in a "safe" zoneif there is little or no leakage through the valve. If there issignificant leakage, the pressure differential across the valve willchange over time, causing the float to move out of the safe zone.

Turning to FIG. 10b, this figure illustrates a different embodiment ofthe tester. In this embodiment, the tester comprises reservoir 82,syringe 41, testing body 42 with viewing ports 42a and 42b, balloon 43,and manometer 44. The reservoir, syringe, balloon, and manometer are allcoupled to the testing body. In addition, the syringe, balloon,manometer, and reservoir all have openings to the tester body which canbe selectively opened or closed.

In this embodiment, to test a valve, the valve is preferably mounted inthe tester body between the balloon and the manometer, such that itopens in the direction of the balloon. Next, the reservoir is filledwith saline. After the valve has been mounted, the syringe 41 is pulledback while only the opening to the reservoir is open, and while theopenings to the balloon and manometer are kept closed. This causes thesyringe to fill up with a known volume of saline, for example 60 cc.Next, the opening to the reservoir is closed, the opening to themanometer is continued closed, and the opening to the balloon is opened.Then, the saline in the syringe is ejected, causing the saline to flowthrough the valve and into the balloon, causing it to expand. At thispoint, just before the balloon recoils, the syringe opening is closed,the reservoir opening is continued closed, and the manometer opening isopened. Since the balloon is preferably calibrated, after receiving theknown volume of saline, e.g., 60 cc, from the syringe, and expanding,the balloon will exert a known pressure, e.g., 120 mm Hg, on the valve.

Next, as the balloon exerts pressure on the valve, any leakage of thesaline through the valve will then enter the manometer. In the exampleof FIG. 10b, the manometer is about 12 cm. long, and is calibrated sothat each 1 cm. equals about 1 cc of leakage. The manometer thusprovides a direct means of measuring the leakage of the valve.

After the manometer is read, it is drained back into the reservoir whilethe opening to the reservoir is opened, and the remaining openings arecontinued closed. Alternatively, it is drained while the syringe (andpossibly reservoir) is opened, and the syringe is retracted, causing thesaline to flow into the syringe. It should be appreciated that in thisembodiment, other means besides a syringe, such as bellows or the like,are possible for injecting saline through the valve.

A third embodiment of a tester is illustrated in FIG. 10c. Asillustrated, this embodiment comprises a double bellows arrangement 45,with the two bellows in the arrangement identified with referencenumerals 45a and 45b. These two bellows are both calibrated and arecapable of displaying a known volume of saline, and generating a knownback pressure on the valve. A valve mount 83 is provided, and is placedon one of the bellows, bellows 45a in the example, which in turn iscalibrated to couple with the mount. Also, means 84 is provided toenable the two bellows to be mated to each other at the valve mount.Further, the outer ends of the two bellows, 46a and 46b, respectively,are clear, enabling a viewer to view the testing process.

In this embodiment, the valve is first mounted on the valve mount 83,and the mount is further positioned within the bellows 45a. Then, one ofthe bellows is used to displace a known volume of saline through thevalve. At this point, a known pressure is exerted on the valve, eitherby a direct pressure exerted by the other bellows, or a vacuum createdby the one bellows. The leakage, if any, of the valve is then visuallyobserved.

Other embodiments of the valve tester are intended to be included, aslong as such an embodiment provides the following three capabilities.First, it must be capable of generating a known closing pressure on thevalve, either by exerting a direct pressure, or by generating a vacuum.Second, it must contain a manometer, a pressure transducer, or othermeans for measuring leakage and pressure differential across the valve.Third, it must provide a quick mount system which is adaptable to allvalve types.

Variants and additions to the tester are also possible. For example, amagnifying lens could be provided in the viewing ports to provideenhanced visual observation of the valve during testing. Or, a lightsource could be added to make it easier to observe the valve undergoingtesting.

Turning back to valve assembly, assuming the valve is acceptable, thevalve is then implanted. At this point, the remaining components in thetwo kits, and the kits themselves, being dispensable, could be thrownaway.

Upon assembly of the valve, the next step is to implant the valve in theannulus. This is accomplished using a holder, with which the surgeon canhold the valve in place while suturing it to the annulus.

While embodiments and applications of this invention have been shown anddescribed, it should be apparent to those skilled in the art that manymore modifications are possible without departing from the inventiveconcepts herein. The invention, therefore, is not to be restricted,except in the spirit of the appended claims.

What is claimed is:
 1. A method of assembling a heart valve, comprisingthe steps of:utilizing a tissue template to cut out at least oneroughly-dimensioned piece of tissue; successively utilizing obturatorsto size an annulus of a heart to be fitted; utilizing aprecisely-configured cutting die to cut the roughly-dimensioned tissueinto precisely-cut tissue having a size appropriate for the annulus tobe fitted; said precisely-configured die being configured with aplurality of ferrules; utilizing said ferrules to cut a plurality ofholes in said precisely-cut tissue; and situating the precisely-cuttissue between first and second stents, one of said first and secondstents being configured with a plurality of tissue alignment membersextending from a surface thereon registering said holes withcorresponding ones of said tissue alignment members.
 2. A method ofassembling a heart valve, comprising:providing a first stent and asecond stent; configuring one of said first and second stents with aplurality of tissue alignment members; extending the tissue alignmentmembers from a surface of one of said first and second stents; providinga tissue cutting die matched in size and shape to said first and secondstents; configuring said tissue cutting die with a plurality offerrules; cutting at least one piece of tissue from a larger piece oftissue utilizing said tissue cutting die while cutting a plurality ofholes in said at least one piece of tissue utilizing said ferrules;registering said holes with corresponding ones of said tissue alignmentmembers; and inducing the first and second stents to clamp said tissuebetween said stents and securely hold it in place.
 3. The method of veryrapidly assembling a heart valve during open heart surgery, comprisingthe steps of:positioning a tissue sizing template formed of a soft andflexible bio-compatible material directly upon the tissue to beharvested; using said template as a guide to cut a piece of thepatient's tissue into a roughly-dimensioned piece of tissue;successively utilizing a series of obturators of different sizes byselectively pushing the obturator into the open annulus of the heart toselect the obturator corresponding to the size of the prosthetic heartvalve to be constructed during the open heart procedure; positioning aprecisely configured cutting die corresponding in size to said selectedobturator proximate to said cut piece of said patient's tissue and,before said tissue is mounted around a stent, utilizing said die to cutsaid roughly-dimensioned piece of tissue into a precisely-cut tissuehaving a size appropriate for said measured annulus so that said tissuemay be mounted between said first and second stents without anyadditional cutting or trimming; situating the precisely-cut tissuebetween first and second stents; and positioning the stents together tosecurely clamp the tissue therebetween.
 4. The method of assembling aheart valve during open heart surgery which is sized to the open annulusremaining after the patient's heart valve has been excised, comprisingthe steps of:providing a first prefabricated, sterile and disposabletissue harvesting and preparing and annulus sizing kit which is notsize-specific to said open annulus and which does not contain anassembled valve, said kit comprising a universal handle; a tissue sizingtemplate having an opening for receiving said universal handle, saidtemplate being formed of a soft and flexible bio-compatible material; aseries of obturators of different size, each obturator having an openingfor removably receiving said universal handle; a first basin for tissuecleaning; a second basin for holding a fixative solution; and a thirdbasin for valve assembly; attaching said universal handle to said tissuesizing template; using said universal handle to position said tissuesizing template directly upon the patient's tissue to be harvested;using said template as a guide to cut a piece of the patient's tissueinto a roughly-dimensioned piece of tissue; cleaning and removing anyfatty deposits from said piece of tissue in said first basin; treatingsaid tissue by brief immersion in a fixative solution in said secondbasin; removing said universal handle from said tissue sizing templateand selectively attaching said handle to said obturators; using saidhandle to push the connected obturator into said open annulus; selectingthe obturator corresponding to the size of said open annulus; selectinga second, prefabricated, sterile and disposable kit corresponding to theobturator selected from said first kit, said second kit comprising atray containing, for rapid availability, the following components: aprecisely configured cutting die, an inner and an outer stent, and anassembly mandrel, each of said components corresponding in size to saidselected obturator; positioning said cutting die adjacent saidroughly-dimensioned piece of tissue and, before said tissue is mountedaround one of said stents, utilizing said cutting die to cut said tissueinto a precisely cut piece of tissue; mounting said tissue around saidinner stent in said third basin; and utilizing said mandrel to locatesaid second stent to permanently situate said tissue between said innerand outer stents and form said heart valve without any tissue cutting ortrimming steps after said tissue is removed from said cutting die. 5.The method of assembling a heart valve during open heart surgery whichis sized to the open annulus remaining after the patient's heart valvehas been excised, comprising the steps of:providing a firstprefabricated, sterile and disposable tissue harvesting and preparingand annulus sizing kit which is not size-specific to said open annulusand which does not contain an assembled valve, said kit comprising atissue sizing template, a series of obturators of different size, afirst basin for tissue cleaning; a second basin for holding a fixativesolution; and a third basin for valve assembly; using said template as aguide to cut a piece of the patient's tissue into a roughly-dimensionedpiece of tissue; cleaning and removing any fatty deposits from saidpiece of tissue in said first basin; treating said tissue by briefimmersion in a fixative solution in said second basin; selectivelypushing said obturators into said open annulus; selecting the obturatorcorresponding to the size of said open annulus; selecting a second,prefabricated, sterile and disposable kit corresponding to the obturatorselected from said first kit, said second kit comprising a traycontaining, for rapid availability, the following components: aprecisely configured cutting die, a first and a second stent, and anassembly mandrel, each of said components corresponding in size to saidselected obturator; positioning said cutting die adjacent saidroughly-dimensioned piece of tissue and, before said tissue is mountedaround one of said stents, utilizing said cutting die to cut said tissueinto a precisely cut piece of tissue; mounting said tissue around saidfirst stent in said third basin; utilizing said mandrel to locate saidsecond stent to permanently situate said tissue between said inner andouter stents and form said heart valve without any tissue cutting ortrimming steps after said tissue is removed from said cutting die. 6.The method of assembling a heart valve during open heart surgery whichis sized to the open annulus remaining after the patient's heart valvehas been excised, comprising the steps of:providing a firstprefabricated, sterile and disposable tissue harvesting and preparingand annulus sizing kit which is not size-specific to said open annulusand which does not contain an assembled valve, said kit comprising atissue sizing template and a series of obturators of different size;using said template as a guide to cut a piece of the patient's tissueinto a roughly-dimensioned piece of tissue; selectively pushing saidobturators into said open annulus; selecting the obturator correspondingto the size of said open annulus; selecting a second, prefabricated,sterile and disposable kit corresponding to the obturator selected fromsaid first kit, said second kit comprising a tray containing, for rapidavailability, the following components: a precisely configured cuttingdie, a first and a second stent, and an assembly mandrel, each of saidcomponents corresponding in size to said selected obturator; positioningsaid cutting die adjacent said roughly-dimensioned piece of tissue and,before said tissue is mounted around one of said stents, utilizing saiddie to cut said tissue into a precisely cut piece of tissue; mountingsaid tissue around said first stent; utilizing said mandrel to locatesaid second stent to permanently situate said tissue between said innerand outer stents and form said heart valve without any tissue cutting ortrimming steps after said tissue is removed from said cutting die. 7.The method of assembling a heart valve during open heart surgery whichis sized to the open annulus remaining after the patient's heart valvehas been excised, comprising the steps of:providing a firstprefabricated, sterile and disposable tissue harvesting and preparingand annulus sizing kit which is not size-specific to said open annulusand which does not contain an assembled valve, said kit including aseries of obturators of different size; cutting a piece of tissue into aroughly-dimensioned piece of tissue; selectively pushing said obturatorsinto said open annulus; selecting the obturator corresponding to thesize of said open annulus; selecting a second, prefabricated, sterileand disposable kit corresponding to the obturator selected from saidfirst kit, said second kit comprising a tray containing, for rapidavailability, the following components: a precisely configured cuttingdie, a first and a second stent, and an assembly mandrel, each of saidcomponents corresponding in size to said selected obturator; positioningsaid cutting die adjacent said roughly-dimensioned piece of tissue and,before said tissue is mounted around one of said stents, utilizing saiddie to cut said tissue into a precisely cut piece of tissue; mountingsaid tissue around said first stent; and utilizing said mandrel tolocate said second stent to permanently situate said tissue between saidinner and outer stents and form said heart valve without any tissuecutting or trimming steps after said tissue is removed from said cuttingdie.
 8. The method of assembling a heart valve during open heartsurgery, comprising the steps of:positioning a tissue sizing templateformed of a soft and flexible bio-compatible material directly upon thetissue to be harvested; using said template as a guide to cut a piece ofthe patient's tissue into a roughly-dimensioned piece of tissue;cleaning and removing any fatty deposits from said piece of tissue in afirst basin; treating said tissue by brief immersion in a fixativesolution in a second basin; rinsing said piece of tissue in a thirdbasin; successively utilizing a series of obturators of different sizedby selectively pushing the obturator into said open annulus to selectthe obturator corresponding to the size of the prosthetic heart valve tobe constructed during the open heart procedure; positioning a preciselyconfigured cutting die corresponding in size to said selected obturatorproximate to said cut piece of said patient's tissue and, before saidtissue is mounted around a stent, utilizing said die to cut saidroughly-dimensioned piece of tissue into a precisely-cut tissue having asize appropriate for said measured annulus so that said tissue may bemounted between said first and second stents without any additionalcutting or trimming; mounting said tissue around said inner stent in afourth basin; and locating said second stent to permanently situate saidprecisely-cut tissue between said first and second stents and securelyclamp the tissue therebetween.